This invention relates to endless ink-ribbon cartridges which recently have found widespread use in typewriters and in high-speed printers utilized in information processing systems.
One cartridge of this type, for example, is described in the Italian patent application No. 24128A/76, filed June 10, 1976, and assigned to the assignee to the instant application, and subsequently filed in the United States on Dec. 13, 1976, as application Ser. No. 750,033 by F. Carlevaro and A. Gaboardi, as signed to the assignee of the instant application.
Such cartridges employ the principle of storing the ink-ribbon in random manner in an internal housing. Because of this fact, the quantity, or length, of ribbon which can be stored is less than the quantity which can be stored on a reel of equivalent dimensions on which, the ribbon is wound in a uniform manner.
A consequence of this random form of storage is a limited ribbon life, due to exhaustion of the ink with which the ribbon is impregnated or due to the actual wearing out of the ribbon. While the exhaustion of the ink can be obviated by disposing reinking devices in the cartridge, the problems of the wearing out of the ribbon have been found to be remedied only by using ribbons of greater length.
It is known that for ribbons formed into a closed loop, an equivalently greater length of ribbon can be obtained by utilizing a ribbon of greater width connected to provide in the ribbon an inversion or twist of 180.degree., in a manner to form a Mobius loop. Such a technique enables the use of two parallel bands of the ribbon for the printing, and the passage from one of the bands to the other occurs without discontinuity by taking advantage of the properties of the Mobius loop.
In order to exploit such an expedient, it is necessary that the ribbon inversion be confined to a well-defined position in the path of the ribbon, and that the inversion move along the ribbon as the ribbon moves along such path, even as the ribbon exits from and reenters into the cartridge.
In the French Pat. No. 2,165,444, published Aug. 3, 1973, for example, there is described an endless ink-ribbon cartridge wherein the ribbon is connected in the form of a Mobius loop; For such cartridge the inversion of the ribbon is effected externally to the containing cartridge in a zone of the printer provided with guide elements disposed downstream and upstream of the inversion zone. The inversion is readily effected between such guide elements by virtue of the relative pliability of the ribbon. However, this approach has the disadvantage of requiring a manipulation of the ribbon that is preferably avoided and of requiring, in addition, a free zone for the inversion of length at least five times the width of the ribbon to assure appropriate inversion of the ribbon.
The French Pat. Nos. 2,276,939 and 2,291,037, published respectively Mar. 5, 1976, and July 16, 1976, describe other cartridges in which such disadvantages of manipulation of the ribbon is avoided. In one of such patents use is made of an appropriate guide which is an integral part of the cartridge, and in the other of these patents the inversion is effected in an appropriate compartment provided in the cartridge.
In order to assure that the inversion occurs properly and does not migrate out of the zone, or compartment, in which it is intended that the inversion should occur, transverse guides are disposed in a median position of the inversion zone. These guides form a slot or a kind of drawplate oriented perpendicularly to the direction of movement of the ribbon and to the plane along which the ribbon would continue to move, absent the inversion.
However, even such expedients are not entirely satisfactory because such an arrangement requires that the edges of the ribbon be stretched relative to the central portion thereof in order to follow a path of greater length. Such stretching tends to cause a folding of the ribbon on itself, particularly if the ribbon is partially worn from use, with the consequent migration of the inversion outside of the zone provided or with the more serious consequence of the jamming of the cartridge.
These disadvantages are minimized only partially by providing an inversion zone sufficiently long to require only a minimum of stretching of the edges relative to the central portion of the ribbon.
Accordingly, it is the object of the present invention to provide an ink-ribbon cartridge which obviates the above-mentioned disadvantages of prior art ink-ribbon cartridges.
Another object of the present invention is to provide an ink-ribbon cartridge wherein unequal stretching of the ink-ribbon elements is avoided.
Another object of the present invention is to provide an ink-ribbon cartridge of the type in which the ink-ribbon is connected in the form of a Mobius loop wherein the inversion is effected in a manner to reduce the frictional drag on the ink-ribbon.
Another object of the present invention is to provide an ink-ribbon cartridge of the type in which the ink-ribbon is connected in the form of a Mobius loop wherein the central portion of the ink-ribbon is stretched slightly more than the edges thereof in effecting the required inversion.